Readout settings tenths vs thousandths

Writing you own would be an advantage. My coding ability is just a bit less than ZERO. I thought it was a major accomplishment when I got my TRS80 to say "hello world".
 
In a digital display of data, given everything else is accurate, the error can be as much as plus or minus a half a count (the least digit). There is really no way around this. So if you display to thousandths, you'll be within one thousandth of the right answer, but can't be sure at less than that. Similarly, if your count is really 2 tenths, 0.0002, you'll be within 2 tenths, but can't resolve closer. So for me, there's value in displaying as much resolution as possible.

Of course, not everything else is that accurate anyway. We usually have more precision than accuracy.
 
Winegrower said:
In a digital display of data, given everything else is accurate, the error can be as much as plus or minus a half a count (the least digit). There is really no way around this. So if you display to thousandths, you'll be within one thousandth of the right answer, but can't be sure at less than that. Similarly, if your count is really 2 tenths, 0.0002, you'll be within 2 tenths, but can't resolve closer. So for me, there's value in displaying as much resolution as possible.

Of course, not everything else is that accurate anyway. We usually have more precision than accuracy.
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It depends on the DRO.
Many Chinese DROs, especially the older ones, use integer math on display units. I.e. the reading is formatted first and then the DRO performs the calculations. "Formatting" can mean proper rounding, or just cutting of of the last digit, depending on the chip the DRO uses. Floating point math is slow and the hardware is relatively more expensive. I.e. in the worst case scenario, 0.1119" (2.842mm) becomes 0.111" (2.819mm), or 23um error before any fancy trigonometry even got involved.
TouchDRO uses double precision floating point math on native data, and formats the output after the calculations are done. This will result in rounding error of +/- 0.0005", or 12um regardless of what you did to the numbers.

For what it's worth, I don't see any reason to use 3 digits with scales that can resolve 4 digits, especially with TouchDRO. There is no performance impact, and regardless of your mill's rigidity, the closer to nominal dimension you start the better chance you get to hit the desired tolerances.
 
ycroosh said:
It depends on the DRO.
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Yep, completely agree. I've been very skeptical of the math in the D80, especially in diameter mode. I did some of the math packages for the early HP calculators, when there were no preexisting library modules, and it's definitely not a trivial problem. Your math I'm sure is way better than what's in my DRO.
 
Hmmm, so far a lot of good information on precision and accuracy. It sounds like the prevailing opinion is to trust the DRO as it is accurate within its limits. After all this info I realize that the DRO is telling me the truth when it is set to show tenths. The relative accuracy of my X2D mill is not necessarily as limiting as I thought. The determining factor on whether to show tenths or thousandths is the accuracy I am trying to achieve with a particular operation and not my perception of my Mill's capabilities.
 
Razzle said:
Hmmm, so far a lot of good information on precision and accuracy. It sounds like the prevailing opinion is to trust the DRO as it is accurate within its limits. After all this info I realize that the DRO is telling me the truth when it is set to show tenths. The relative accuracy of my X2D mill is not necessarily as limiting as I thought. The determining factor on whether to show tenths or thousandths is the accuracy I am trying to achieve with a particular operation and not my perception of my Mill's capabilities.
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You probably noticed that crapping on the mini mill is a whole hobby in itself within the hobby machining community :) The X2 platform definitely has shortcomings, but there is nothing that makes it inherently inaccurate. My main mill is a 2/3 Bridgeport clone from PM (PM-935VT), but I still have a mini mill that I use for small high precision work. I put some work into it to make it fit my needs:
  • Scraped the ways to remove binding
  • Added lubrication ports
  • Replaced spindle bearings with ABEC5 angular contact bearings
  • Replaced the DC motor with a Custom Crafter BLDC motor kit (they are a sponsor on this forum, BTW)
  • Added 20LB of bird shot (with epoxy) to the head to make it heavier, so it always "droops" to remove the Z axis backlash.
If you respect the size/limitations of the machine, it is capable of very accurate work. Definitely better than +/-0.001", and definitely not any less accurate than a Bridgeport (if you find someone with a Bridgeport, measure the effect of table droop when you move it from one side to another. You'd be surprised...).

Regards
Yuriy
 
Razzle said:
This is more of a survey than a question. I have 5 micron glass scales on my Seig X2D minimill. Since calibration I have left the readouts set to display down to tenths. Sometimes I get confused and read the tenths as thousandths. My question for everyone is what do you keep your readouts set to display? I highly doubt that tenths has any meaning on my X2D. So is there any value on keeping the display set to show tenths?
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I am set to 0.00001, I shoot for 0.001 typically but I like the additional digits as I can see what is happening. If you have it set to 0.001 and it is 0.00187, it might as well be 0.002 but I cannot tell if the smallest I see is 0.001.
 
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